Electronic components continue to be reduced in size. Unfortunately, direct current power supplies for such electronic components have not undergone such size reductions. Specifically, it is now common for small portable electronic components such as portable computers to have accompanying power supplies that are substantial in size and weight comparable to the portable computers themselves.
Conventional power supplies that rectify 50/60 Hertz 120/220 volt alternating current into direct current are particularly large. Such devices usually include full wave or half wave rectifiers which produce direct current still having the "ripple" of the originating alternating current. Thereafter, this ripple in the rectified current is substantially eliminated by appropriate electronic circuitry, such as a capacitance and inductance, to produce the required stable direct current.
Unfortunately, such conventional power supplies involved low frequencies and long wave lengths. These low frequencies and long wave lengths lead to high power losses. Almost everyone using such devices is familiar with the "warm" feeling that such large rectification devices have after continued use. Further, such components have large size. They either occupy a substantial volume of the devices which they power or alternatively constitute large stand alone components which reside outside of the units which they power.
In an effort to further reduce size, so-called switched mode power supplies have been utilized. These devices include a low frequency rectifier and relatively crude filter. The total power from this low frequency rectifier and filter is then routed to a semiconductor switch. With the semiconductor switch, the rectified power is then converted to high frequency switched power which is thereafter rectified.
These switched power supplies generally operate with their switching transistors operating in the kilohertz range--typically below 40 KHz. While the ultimate rectification that they can produce is superior, and the rectifying components of such power supplies are somewhat smaller, they frequently are not equivalent in size to the components that they serve. For example, the average "notebook computers" single largest component is the power supply. It is almost always, external to the remainder of the computer and rather bulky relative to that computer.